Operating method for a solid fuel burner

ABSTRACT

The invention belongs to the engineering domain of heating systems, in particular heating systems for chipped to free-flowing fuels in solid form and relates to an operating method for a solid fuel burner. The aim of the invention is to design an operating method for a solid fuel burner, which achieves an efficient operating mode for said burner with the main focus on minimizing the production of aggressive substances such as acids. To achieve this, according to the invention, the burner operation has a double or triple combustion phase profile and the burner operates with two different groups of combustion material.

The present invention appertains to the technical field of firing systems, thus to the field of firing systems for lumpy to free-flowing fuels in solid form, and it particularly relates to an operating method for a solid fuel burner.

It is prior art to process lumpy materials such as pellets or small sized to free-flowing bodies, e.g. stones or grains from a biogenic material, as fuel in solid fuel burners. Either gravity or specific conveyor systems are used for the purpose of supplying such lumpy to free-flowing fuels to the solid fuel burner. As a rule, the combustion inevitably generates under certain circumstances undesired or harmful substances. Thus, aggressive substances such as acids are formed in combustion chambers and downstream chambers, which are still in a cold state, and if the combustion gases are still cold. These acids cannot but result in the damage of the entire system because a condensation cannot be prevented under such operating conditions. In the relevant category of solid fuel burners and the operating methods thereof and, thus, in the underlying service temperature range or temperature regime, respectively, it is impossible to eliminate the aforementioned formation itself. According to the assessment of the prior art this problem has, so far, not yet been solved in a satisfactory manner.

The technical solution disclosed in EP 1 396 679 A1 describes a transport of the fuels initially in the reservoir by means of a screw. Next, they are pneumatically fed by means of negative pressure to a remotely positioned heater and are then supplied to the combustion chamber by means of an electromechanical quantity dosage. The operating method is not included in this technical solution.

Document DE 20 2005 003 836 U1 describes a rotationally symmetrically designed warm-air heater for heating a gas by means of a solid fuel burner which burns biogenic material. The invention relates to the combination of a heat source in the form of a solid fuel burner and a heat exchanger in one, wherein the technical teaching describes the realization of the circulation of the combustion gases in trains and that of the air to be heated by means of heat exchanger construction elements.

Document AT 413 881 B describes a system solution comprised of a heating boiler with a heat exchanger, a solid fuel burner, an ignition device, an air supply device as well as storage and supply devices for the fuel. This technical solution mainly deals with an automatic ignition device and the secure operation thereof in interaction with others. In as far as this technical solution relates to combustion at all, nothing is said about the operating method.

According to AT 003 685 U1 and AT 410 364 B and pertinent DE 200 07 801 U1 a solid fuel burner is described, which comprises an underfeed device located underneath the combustion chamber housing, but not the control of the combustion process.

Starting out from the deficiencies of the aforementioned prior art the invention is based on the object to obtain an improved and efficient operating mode of the solid fuel burner by means of which the formation of aggressive substances such as acids is minimized.

According to the invention this object is achieved with the features of the main claim, with an advantageous embodiment being defined by the features of the dependent claim.

The following description shall particularly point out the advantageous effects of the method according to the invention.

A prerequisite for the operating method according to the invention is a burner, e.g. a likewise inventive solid fuel burner, which is configured as a hollow cylindrical, multiple-divided burner comprising tube parts which are arranged on a common axis, with the slag being discharged laterally in the axial direction, for two kinds of combustion materials, said burner comprising at least two entries, which may be also be located slightly remote of the burner, approximately 1 m.

The one combustion material entry is provided for coarser biogenic combustion materials such as chippings, cereal wastes and strip wastes. The other combustion material entry of the overall assembly is provided for small sized to free-flowing bodies such as stones or grains from a biogenic combustion material. If the two combustion material entries are provided as multiway entries it is also possible to optionally supply very different combustion materials to the combustion. Thus, combustion materials that do not release any aggressive substances can initiate the combustion process while, in the following, combustion materials may be used in the combustion process that are to be combusted for various reasons, but that would initially release aggressive substances in the starting process of the combustion.

The operating method according to the invention is provided as a multiphase combustion operation, specifically as a 2- or 3-combustion phase operation. To this end it is also provided that the burner operates with two different groups of combustion material. One combustion material group 1 comprises biogenic combustion material that does not form any aggressive substances, e.g. acids, during its combustion at a temperature below the burner operating temperature applicable to the burner, for example, pure wood combustion materials. One combustion material group 2 then comprises all other biogenic combustion materials, e.g. straw, cereals, rape, corn, miscanthus, cherry stones.

The start of the burner, phase 1 of the burner operation, is accomplished with a starting combustion material of the combustion material group 1. To this end, the combustion material is supplied from a combustion material entry separately predetermined for this purpose, while the second combustion material entry for the main combustion material of combustion material group 2 is initially not yet active. Upon reaching the operating temperature of the burner the combustion material supply at the combustion material entry for combustion material group 1 is deactivated. Instead, the combustion material supply at the combustion material entry for the main combustion material, combustion material group 2, is activated.

The continuous operation of the burner is then continued—provided that its temperature is not below its operating temperature—wherein, if the combustion material entry of this combustion material group is alternatively configured as a multiway entry, it can combust alternative combustion materials in combustion material group 2 clocked with respect to time or in dependence on other conditions, phase 2 of the burner operation.

The termination of the combustion process, phase 3 of the burner operation, when the burner is currently in the state of combusting combustion material of combustion material group 2, is performed in such a way that initially the combustion material supply of combustion material group 2 is deactivated and the combustion material supply of combustion material group 1 is activated, and that the combustion is then stopped out of this combustion material group, phase 3 of the burner operation.

In the 2-combustion phase operation the combustion operation is stopped in phase 2, i.e. during the combustion of combustion material group 2.

As was already partially set forth in connection with combustion phase 2, the combustion process can basically be performed alternately with combustion materials in combustion material group 2 and/or alternately between combustion material groups 1 and 2.

The invention shall be explained in more detail by means of the following embodiment.

FIG. 1 represents an already described solid fuel burner which forms part of a heating or warm water system/warm water conditioning system not illustrated in more detail.

Two entries 7 a and 7 b for the combustion material are provided on the tube part 3 which is arranged on the outside. Combustion material entry 7 b is provided for the supply of coarser solid biogenic combustion materials, e.g. chippings, cereal wastes and strip wastes, into the combustion chamber. Combustion material entry 7 a is provided for small sized to free-flowing solids, cereal grains, cherry stones etc. These combustion material entries may also be located slightly remote of the combustion chamber and can then be introduced into the combustion chamber by a “central” tube.

EMBODIMENT

Biogenic material for operating a heating system is to be combusted by means of a solid fuel burner, which is exemplarily illustrated for this method in FIG. 1. Any other solid fuel burner having at least two combustion material entries is suited for this purpose.

Phase 1 of the combustion operation starts as soon as the control software of the heating system sends a heating and/or hot water request to the boiler, and it will activate a combustion material transport from the silo via the combustion material entry for combustion material group 1 into the combustion chamber. To this end, a specific time period is specified, e.g. 30 sec., which corresponds to the exact on-site conditions. Simultaneously with the transport of, for example, wood pellets, or slightly time-shifted afterwards, the hot-air blower is started and supplies hot air via connection 9, hot air blower. It has a minimum power of, for example, 2000 watt and generates hot air of approximately 600° C. The run time is limited to a maximum of six minutes. 30 sec. after the hot air blower has started the combustion gas ventilator is started, that is, an airflow is generated which supports the ignition of the pellets. As soon as an oxygen sensor detects a reduction of the oxygen concentration to below approximately 15% because the pellets are combusting, the hot air blower is switched off. As soon as the oxygen concentration has dropped below 12%, again, pellets are supplied for 30 sec. Then, the control system waits for 90 sec. and supplies pellets again for 30 sec. This process is repeated five times. Upon the termination of these processes it is switched to “intelligent” control, i.e. the combustion gas ventilator continuously provides via a negative pressure and a PID-controlled ventilator speed for a negative pressure at the combustion gas pipe of, in this case, 40 to 60 pascal, and this depending on the purpose of use, other device-related conditions and downstream heat exchanger, so that also higher negative pressures may be necessary, e.g. 1000 to 2000 pascal. A specific oxygen concentration, e.g. 9.5% depending on the combustion material etc., is set at the oxygen sensor. By means of the actual-versus-setpoint comparison the control system calculates the ratio between the run time and the standstill of the screw; averaging 60 sec. If the combustion is optimal, the burner slowly reaches its maximum power. As long as the backflow elevation is closed (boiler water is not delivered into the heating network because it is still too cold) only combustion materials of group 1—wood pellets—are combusted. As soon as the backflow elevation is opened or the combustion gas temperature has reached a specific predetermined value, e.g. 150° C., the supply of further wood pellets is stopped, termination of the combustion process, phase 1, and the other combustion material entry for combustion material group 2—main combustion material, e.g. straw pellets—is activated, start of the combustion process, phase 2. As soon as the burner request from the control system stops, the combustion process, phase 3, is initiated, that is, the combustion material entry for combustion material group 2—main combustion material, e.g. straw pellets—is deactivated and the combustion material entry for combustion material group 1 is reactivated. Thus, it is ensured that during the ongoing combustion of “pure” wood pellets residues of the combustion material generating the aggressive substances are completely burnt and that, thus, polluted combustion gases have been withdrawn from the burner and the combustion gas channel. Under certain current combustion conditions the combustion operation can also be stopped in phase 2, that is, by omitting phase 3. 

1. Operating method for a solid fuel burner, characterized in that the start of the burner is performed with a starting combustion material—combustion material group 1—which does not form aggressive substances such as acids at a temperature below the burner operating temperature applicable to the burner, that, to this end, the combustion material is supplied from a first combustion material entry (7 a) predetermined for this purpose, wherein the second combustion material entry (7 b) for the main combustion material—combustion material group 2—is initially not yet active, that upon reaching the operating temperature of the burner the combustion material supply at said first combustion material entry (7 a) is deactivated and, instead, the combustion material supply at the second combustion material entry (7 b) for the main combustion material is activated, that the continuous operation of the burner is continued—provided that its temperature is not below its operating temperature—wherein, if the second combustion material entry (7 b) is configured as a multiway entry, it can be supplied with alternative combustion materials in combustion material group 2 clocked with respect to time or in dependence on other conditions and can be performed clocked with respect to its operation, that the termination of the combustion process, when the burner is currently in the state of combusting combustion material of combustion material group 2, is performed in dependence on the current combustion conditions either in such a way that initially the combustion material supply of combustion material group 2 is deactivated and the combustion material supply of combustion material group 1 is activated, and that the combustion is then stopped out of this combustion material group, or that the combustion is stopped in the state of combusting combustion material of combustion material group
 2. 2. Operating method according to claim 1, characterized in that the combustion process is performed alternately with combustion materials in combustion material group 2 and/or alternately between combustion material groups 1 and
 2. 